This invention relates generally to a method for treating the distilled water obtained from an evaporation process sea water desalination plant.
Typically, the distilled water obtained as a result of evaporation desalination processes is devoid of minerals, leading to the corrosion of water handling apparatus and lacking taste as drinking water. A solution to the problem has been to convert the distilled water to a more suitable quality by dissolving carbon dioxide and calcium carbonate or calcium hydroxide into the distilled water. The expense of obtaining the quantity of carbon dioxide necessary to treat the water has been a disadvantage, however.
Conventionally, carbon dioxide has been produced utilizing processes unrelated to that of the desalination plant by burning fuel oil or fuel gas. The enormous expense and running costs of such a separate facility are, however, prohibitive.
An improvement on the conventional method of producing carbon dioxide shown in Japanese Patent Provisional Publication No. 55-35971, makes use of the phenomenon that carbon dioxide is generated when acid such as hydrochloric or sulfuric is added to salt water. Before beginning the desalination process, acid is added to the salt water which is then fed into a decarbonator. Carbon dioxide is extracted from the decarbonator, which is at high vacuum (about -600 mmHg), with a vent ejector, requiring a large quantity of high pressure steam. The steam must then be condensed out, requiring a large quantity of cooling water. Although this method is an improvement over the conventional method of generating carbon dioxide in a completely separate process, the large quantities of steam and cooling water required by this method are disadvantageous. In addition, ammonia gas resulting from pyrolysis of hydrazine from the use of deoxidizers typically found in high pressure steam systems may ultimately contaminate, with unacceptable levels of ammonia nitrogen, the distilled water to which carbon dioxide generated from this method is added.